1. Field of the Invention
The present invention relates generally to an internal combustion engine equipped with a supercharger and an idling speed control system, and more particularly, to an internal combustion engine which is equipped with a supercharger in an inlet channel in which an intercooler and a throttle valve are also disposed at the downstream portion thereof compared with the supercharger and with an idling speed control system containing a bypass channel connected with the inlet channel to detour the throttle valve.
2. Description of the Prior Art
There has been proposed an internal combustion engine used for an automobile which is provided with an idling speed control system for controlling idling speed of the engine in response to operating conditions of the same for the purpose of restricting the idling speed as low as possible without causing engine stop under a condition wherein the engine operates with appendant loads, such as an air conditioner, so as to improve fuel consumption and advancing warming-up of the engine after a cold start of the same. In the idling speed control system, a bypass channel with an air flow control valve installed therein is provided for detouring a throttle valve installed in an inlet channel of the engine and the air flow control valve is controlled in its opening degree to adjust intake air mass flow supplied to the engine during an idle operation of the engine, so that the idling speed is maintained to be a target idling speed set in response to actual operating conditions of the engine.
It has been also proposed to apply such an idling speed control system as mentioned above to an internal combustion engine equipped with a supercharger which is operative to augment output power of the engine, as disclosed in, for example, the Japanese patent application published before examination with the publication No. 58-178843. In a previously proposed internal combustion engine which is equipped with a supercharger together with an intercooler which is provided at the downstream portion of an inlet channel compared with the supercharger for cooling intake air compressed by the supercharger in the inlet channel and to which the idling speed control system is applied, a bypass channel for detouring a throttle valve installed in the inlet channel is formed to have one end thereof connected to a portion of the inlet channel immediately downstream from the throttle valve and the other end thereof connected to another portion of the inlet channel immediately downstream from throttle valve, without consideration of a positional relation with the intercooler. For example, in the case of such an engine that has an intercooler provided at the upstream portion of an inlet channel compared with a throttle valve, a bypass channel for detouring the throttle valve is formed with one end thereof connected to a portion of the inlet channel downstream from the intercooler and the other end thereof connected to another portion of the inlet channel downstream from the throttle valve.
In such a previously proposed arrangement, since intake air flows into the bypass channel after passing through the intercooler wherein the intake air is cooled and therefor fuel mixed with the intake air is impeded to evaporate appropriately on the occasion of a cold start of the engine and during an idle operation of the engine after the cold start, the cold start of the engine is apt to be prevented from being carried out smoothly and idling speed of the engine is likely to be unstable or changeable. Further, especially, in the case of such an arrangment that the intercooler is positioned over the engine, the intercooler is heated up to be of relatively high temperature with heat radiated from the engine for a while after the engine is stopped operating, and consequently, if the engine is started to operate again immediately after it is stopped operating once, that is, the engine is subjected to a hot start, intake air flows into the bypass channel after passing through the intercooler wherein the intake air is heated and therefore air charge efficiency is reduced, so that the hot start of the engine is apt to be prevented from being carried out smoothly and idling speed of the engine is likely to be unstable or changeable after the hot start of the engine.